The present invention relates to a portable radio apparatus for a vehicle telephone system or the like and, more particularly, to a portable radio apparatus having a channel scanning function.
A vehicle telephone system, for example, has control channels and audio channels, and a mobile subscriber receiver is tuned to any of the control channels which is in a waiting condition. While an electric field is not developed on the control channel to which the receiver is tuned, the receiver repeatedly performs channel scanning until it finds a control channel with an electric field. A receiver with an implementation for saving power while data reception is under way with an electric field developed is disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 98030/1986, or Patent Application No. 219231/1979, which is assigned to the assignee of this invention and which was laid open on May 16, 1986.
Specifically, the above-mentioned receiver is constructed so that a serially received data stream is converted into parallel data by a serial-to-parallel converter only when parallel outputs of the converter are received, a microprocessor is operated intermittently. Such an intermittent operation of the microprocessor is successful in reducing the power which is consumed by the entire receiver. This prior art receiver, however, suffers from a drawback because battery saving is not guaranteed while received data is absent under a no-field condition, although battery savings are achievable during data reception. More specifically, in a no-field condition, the receiver performs channels scanning continuously in order to acquire a channel on which an electric field is developed thus, causing a receiving section thereof to continuously consume power.